A driving force adjustment apparatus is known to the inventors in which a differential apparatus interposed between the left and right wheels of a vehicle and a motor are combined such that distribution of the driving force (torque distribution) between the left and right wheels can be changed. In such a driving force adjustment apparatus as just described, the motor rotates passively in response to the difference between rotational speeds of the left and right wheels upon turning of the vehicle to absorb the rotational speed difference. Further, as the motor operates actively, the driving force difference between the left and right wheels increases or decreases to change the distribution of the driving force between the left and right wheels (e.g. JP 2007-177915 A, JP 2014-037884 A).
A conventional driving force adjusting apparatus is provided with a motor for adjusting distribution of driving force between the left and right wheels separately from a driving source for driving the left and right wheels. This makes it difficult to reduce the weight and the size of the apparatus and its mountability is liable to worse. The increase in weight of the driving force adjustment apparatus would degrade the operation performance of the vehicle.